Make the 'dirs' tests pass for bash and zsh.

OSH tests fail because the working directory isn't printed.

zsh has one "OK" due to whitespace (it uses tabs instead of spaces.)

spec/builtins2.test.sh

@@ -26,37 +26,43 @@ echo status=$?
# OK mksh stdout-json: "echo\nmyfunc\nstatus=1\n"

### dirs builtin
cd /
dirs
# stdout-json: ""
# stdout-json: "/\n"
# status: 0
# N-I dash/mksh status: 127
# N-I dash/mksh stdout-json: ""

### dirs -c
pushd /
### dirs -c to clear the stack
cd /
pushd /tmp >/dev/null  # zsh pushd doesn't print anything, but bash does
dirs
dirs -c
dirs
# stdout-json: "/\n/\n"
# stdout-json: "/tmp /\n/tmp\n"
# status: 0
# N-I dash/mksh status: 127
# N-I dash/mksh stdout-json: ""

### dirs -v
pushd /
### dirs -v to print numbered stack, one entry per line
cd /
pushd / >/dev/null
dirs -v
pushd /
pushd / >/dev/null
dirs -v
# stdout-json: "/\n 0 /\n/ /\n 0 /\n 1 /\n"
# stdout-json: " 0  /\n 1  /\n 0  /\n 1  /\n 2  /\n"
# status: 0
# zsh uses tabs
# OK zsh stdout-json: "0\t/\n1\t/\n0\t/\n1\t/\n2\t/\n"
# N-I dash/mksh status: 127
# N-I dash/mksh stdout-json: ""

### dirs -p
pushd /
### dirs -p to print one entry per line
cd /
pushd / >/dev/null
dirs -p
pushd /
pushd / >/dev/null
dirs -p
# stdout-json: "/\n/\n/ /\n/\n/\n"
# stdout-json: "/\n/\n/\n/\n/\n"
# N-I dash/mksh status: 127
# N-I dash/mksh stdout-json: ""